An arithmetic number sequence is a number pattern where a constant difference, d, is added to each term to arrive at the next. You can describe any arithmetic sequence either explicitly, where the n'th term can be found immediately, or recursively, which is where you must know the "n - 1'th" term in order to find the n'th term. Both types of formulas depend on knowing the difference, d. Here we practice writing both explicit and recursive formulas for the same number pattern.